So here's the deal. This question was posted in a separate, closed thread and the answer provided was incorrect. Therefore, since I did the research when making my purchase, came across the question in my search, and found the correct answer, I wanted to provide that for the next person that searches for it.
The model numbers refer to two different variations of the HP Spectre x360 15 laptop. Unlike what the previous thread suggested, both of these models ARE 2-in-1 notebooks. The difference, based on a website comparison, is in the I/O ports.
In addition to everything the 7PU81AV_1 model has, the 191B0AV_1 appears to also have another USB-C port, a mini DisplayPort, and an RJ-45(ethernet) port. Hope that helps the next person.
Both of them are for the Envy 15t-eb000 CTO machines. The differences: depending on when, you can get better deal or better options. For example you can more RAM and storage for one set and less expensive
one with 8 GB memory; 256 GB SSD storage another one is cheaper (more discount) with 16 GB memory; 512 GB SSD storage
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